In the processing and packaging of semiconductor devices, wire bonding continues to be the primary method of providing electrical interconnection between two locations within a package (e.g., between a die pad of a semiconductor die and a lead of a leadframe). More specifically, using a wire bonder (also known as a wire bonding machine) wire loops are formed between respective locations to be electrically interconnected. The primary methods of forming wire loops are ball bonding and wedge bonding. In forming the bonds between (a) the ends of the wire loop and (b) the bond site (e.g., a die pad, a lead, etc.) varying types of bonding energy may be used, including, for example, ultrasonic energy, thermosonic energy, thermocompressive energy, amongst others. Wire bonding machines (e.g., stud bumping machines) are also used to form conductive bumps from portions of wire.
During ball bonding operations, a tail of wire extending from the tip of a bonding tool (e.g., a capillary) is melted into a free air ball using a spark from an electronic flame-off (EFO) device. The free air ball is then used to form a first bond (e.g., a ball bond) at a first bonding location, and the wire is extended from the ball bond to a second bonding location, where a second bond (e.g., a stitch bond) is formed by bonding a portion of the wire to the second bonding location using the bonding tool. For example, the first bonding location may be a bonding pad of a semiconductor chip, and the second bonding location may be a lead of a leadframe adjacent a semiconductor chip. The bonding tool may then be raised to a short tail detect height where the wire is tested (e.g., using an electrical continuity test) to ensure it is still continuous with the stitch bond on the second bonding location. If no short tail is detected, the bond head (i.e., carrying the bonding tool and a wire clamp, now closed) is raised to tear the wire at the stitch bond. The remaining tail length may then be used to form another free air ball for another wire loop.
Specifically referring now to FIGS. 1A-1J, a conventional method of forming a wire loop is illustrated. FIG. 1A illustrates parts of a wire bonding machine 100 including bonding tool 102 (e.g., capillary 102), wire clamps 104 (in an open position in FIG. 1A), wire 106, and free air ball 108 having been formed and seated at tip 102a of bonding tool 102. In FIG. 1A, bonding tool 102 is shown moving towards first bonding location 114 (e.g., bond pad 114 of a semiconductor die) as indicated by the downward arrow. Wire 106 is continuous with free air ball 108 and extends through bonding tool 102 and back to a wire supply (e.g., a wire spool, not shown) on wire bonding machine 100. At FIG. 1B, first bond 112a (e.g., ball bond 112a) is formed on first bonding location 114 using free air ball 108. In the illustrated example, first bond 112a is formed with wire clamps 104 in an open position. At FIG. 1C, bonding tool 102 is raised (with wire clamps 104 in an open position) above first bonding location 114 as indicated by the upward arrow. Between the positions shown in FIG. 1C and FIG. 1D, various wire looping motions may be performed as desired in the given application. In any event, at FIG. 1D, bonding tool 102 is raised to position 118 (e.g., a top of loop (TOL) position). At FIG. 1E wire clamps 104 are closed, and a continuity test may be performed to confirm that first bond 112a is bonded to first bonding location 114. After the test at FIG. 1E, bonding tool 102 is moved toward second bonding location 120 (e.g., a lead 120 of a leadframe) as indicated by the downward arrow in FIG. 1F. At approximately the position shown in FIG. 1F, wire clamps 104 may be opened such that during the second bond formation shown in FIG. 1G wire clamps 104 may be open. In FIG. 1H, with wire clamps 104 still open, bonding tool 102 is raised to height 124 (e.g., a tail height for forming a wire tail to be used to form a free air ball for a later wire loop). Wire clamps 104 are then closed to be in contact with wire 106 as illustrated in FIG. 1I, and a continuity test may be performed to confirm that the second bond formed at FIG. 1G is bonded to second bonding location 120. At FIG. 1J, bonding tool 102 has been raised (as indicated by the upward arrow), with wire clamps 104 still closed, to tear the wire from second bond 112b (e.g., a stitch bond), thereby separating the now formed wire loop 112 from wire tail 128 extending below tip 102a of bonding tool 102.
During formation of wire bonds (e.g., a first bond of a wire loop, a second bond of a wire loop, a conductive bump formed from wire, etc.), a non-stick (i.e., no-bond) condition may occur. For example, such non-stick conditions include: (a) a free air ball that does not sufficiently bond to a bond pad (i.e., non-stick-on-pad (NSOP)); and (b) the wire fails to sufficiently bond to a lead (i.e., non-stick-on-lead (NSOL)). Any of these conditions during formation of a wire loop (or a conductive bump) may result in a delay of subsequent operations and costly operator intervention. Such conditions may be caused, for example, by: contamination of a bonding location; variation of the material used to form a bonding location; etc.
Thus, it would be desirable to provide improved methods of performing wire bonding operations including improved methods of forming wire loops and conductive bumps.